In various multistage rotary machines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a gas turbine, for example, a gas is compressed through successive stages in a compressor and mixed with fuel in a combustor. The combination of gas and fuel is then ignited for generating combustion gases that are directed to turbine stages to produce the rotational motion. The turbine stages and compressor stages typically have stationary or non-rotary components, e.g., vanes, that cooperate with rotatable components, e.g., rotor blades, for compressing and expanding the operational gases.
Any fluid leakage between stages reduces overall gas turbine engine performance and efficiency and therefore, interstage seals in seal housings are provided to reduce such leakage. In general, fluid leakage is reduced when the gap between the seal and a rotor assembly is minimized. Labyrinth seals have been used to effect a seal between stages at different pressures in gas turbine engines. Such seals generally comprise two principal elements, i.e., a rotating seal and a static seal. The static seal, as viewed in cross section parallel to the axial length of the engine, frequently has rows of thin labyrinth fingers or teeth, typically formed of stainless steel, extending radially from a relatively thicker base. The teeth of the static seal extend radially to a location adjacent the rotating seal. If contact occurs between the labyrinth teeth and the rotating seal, the stainless steel teeth may harden, and wire-like strips of the tooth material may be liberated from the labyrinth teeth. These so called “seal wires” enter the flow path and may cause significant damage to diaphragm airfoils, often resulting in forced outages to repair the damage. Accordingly, labyrinth seals have generally been designed to allow sufficient clearance to avoid problems associated with contact between the labyrinth teeth and the adjacent seal surfaces, allowing a certain amount of leakage with an associated loss of performance.
It is also known to form the static seal or stator with a honeycomb configuration for cooperating with a rotating seal component, such as a rotary seal arm having a plurality of sharp seal teeth. These principal elements are positioned with a small radial gap therebetween to permit assembly of the rotating and static components. When the gas turbine engine is operated, the rotating seal expands radially more than the static seal and rubs into the static seal. The thin honeycomb construction of the static seal reduces the surface area on which the seal teeth rub and thus helps to minimize the heat transferred into the rotating seal.
It is an object of the present invention to provide a seal construction for a multistage rotary machine that does not require teeth to form a seal between stationary and rotating seal components. It is a further object of the invention to provide such a seal construction in which a gap between seal components may be reduced, and in which heat produced by abrading contact between such components may be minimized.